Validation for PythiaVPhoton10

Jiahang Zhong (Academia Sinica)

23/4/21 DTY bi-weekly meeting, J. Zhong 2

Motivation

W/Zinclusive (5104/5105/5144/5145) were chosen as background samples, in which Pt>25GeV Photons are rare. (110/500,000)

Have more phase space for cuts.

In Pythia, VPhoton processes are singular in the limit Pt->0, hence Pt should not be too small.

23/4/21 DTY bi-weekly meeting, J. Zhong 3

Z Cross Section Table (Electron)

unit [pb]Baur’s

GeneratorPYTHIA

Zinclusive

PYTHIA ZGamma2

5

PYTHIAZGamma10

Electron Channel

s(FSR) [PT(g) > 5GeV & Mee > 40 GeV] 209 193.3

s(FSR) [PT(g) > 10GeV & Mee > 40 GeV]

110.1 104.4

s(FSR) [PT(g) > 15GeV & Mee > 40 GeV]

62.2 61.1

s(FSR) [PT(g) > 25GeV & Mee > 40 GeV]

17.2 20.7

s(ISR) [PT(g) > 5GeV & Mee > 40 GeV] 8.6 11.5

s(ISR) [PT(g) > 10GeV & Mee > 40 GeV]

4.23 6.34 3.90

s(ISR) [PT(g) > 15GeV & Mee > 40 GeV]

2.5 3.7 2.64

s(ISR) [PT(g) > 25GeV & Mee > 40 GeV]

1.14 1.54 1.01 1.28

23/4/21 DTY bi-weekly meeting, J. Zhong 4

Z Plots (Electron)Normalized from 25~200 GeV

Normalized from 10~200 GeV

FSR

ISR

23/4/21 DTY bi-weekly meeting, J. Zhong 5

W Cross Section Table (Electron)

unit [pb]

Baur’s Generat

or(W+g)

Baur’s Generat

or(W-g)

PYTHIA Winclusiv

e(W+g)

PYTHIA Winclusiv

e(W-g)

PYTHIA WGamma

25(W+g)

PYTHIA WGamma

25(W-g)

PYTHIAWGamma

10(W+g)

PYTHIAWGamma

10(W-g)

Electron Channels(FSR)

PT(g)>5GeV600 431 585 412

s(FSR) PT(g)>10GeV

327.8 235.8 323.0 225.2

s(FSR) PT(g)>15GeV

194.0 137.8 196.4 134.9

s(FSR) PT(g)>25GeV

62.1 44.4 74.4 47.9

s(ISR) PT(g)>5GeV

52 37 64 52

s(ISR) PT(g)>10GeV

17.5 12.0 34.3 28.8 9.6 6.5

s(ISR) PT(g)>15GeV

8.83 5.97 20.7 16.9 6.29 4.37

s(ISR) PT(g)>25GeV

3.18 2.17 8.79 6.91 2.10 1.36 2.92 2.06

23/4/21 DTY bi-weekly meeting, J. Zhong 6

W Plots (Electron)Normalized from 25~200 GeVNormalized from 10~200

GeV ISR

FSR

23/4/21 DTY bi-weekly meeting, J. Zhong 7

Control Tags for a new sample In pythia, adjust PYSUBS-CKIN3 from 25 to 10.

CKIN3: Pt lower limit in the rest frame of hard interaction.

In GeneratorFilter, adjust PhotonFilter.Ptcut from 25000 to 10000.

PhotonFilter.Ptcut: (GenStat==1&&Pt>25GeV) photon in pythia output

In additional, PhotonFilter requests Photon Eta<2.7.

All 3 leptonic decay channels are turned on.

23/4/21 DTY bi-weekly meeting, J. Zhong 8

Cross Section Comparisonapplied selection cuts

Two cuts are used to select Pt>25GeV events from VPhoton10 samples.

#1 Lab frame Pt Cut (as Generator Filter) Require Type==22 & GenStat==1 & Pt>25GeV With-filter samples only

#2 W+Gamma Rest frame Pt cut (as CKIN3) KOriVNt==4 & GenStat==3 Boost 2 particles to their CM frame After boost, require Pt>25GeV

For samples with filter, both cuts are usedFor samples without filter, only cut #2 are applied

23/4/21 DTY bi-weekly meeting, J. Zhong 9

Cross Section ComparisonWGamma

Both Filtered and Non-Filter samples are tested.

Non-100% selection for WPhoton25 samples indicates problem with CKIN3 definition

Similar discrepancy observed among the comparison between 10GeV/25GeV/40GeV no-filter samples with cut on 40GeV

Zgamma has same discrepancy

WPhoton25 WPhoton10

With Filter

Cut #1 & #2

No Filter

Cut #2

With Filter

Cut #1 & #2

No Filter

Cut #2

σ(total) 7.41pb 11.5pb 32.8pb 52.3pb

Cut efficiency 96.5% 91.0% 27.7% 28.3%

σ(output) 7.2pb 10.5pb 9.1pb 14.7pb

23/4/21 DTY bi-weekly meeting, J. Zhong 10

Cross Section ComparisonCKIN3 comparison

Log histogram for CKIN3 value (Photon Pt in rest frame)

Tails below cuts imply distortion of original kinematics.

WPhoton25 histogram is normalized to WPhoton10’s scale

Visible different slopes responsible for cross-section shift

23/4/21 DTY bi-weekly meeting, J. Zhong 11

Meaning of CKIN3discussion in MC hyper news (1)

Inspiring discussion in the MC generators HN, still undergoing…https://hypernews.cern.ch/HyperNews/Atlas/get/Generators/60.html

First suggestions to play with MSTP 61 & 91 tags. MSTP 61: ISR switch. Default=2 as on. Switch to 0 as off.

Correction as underlying events, rather than switch for our ISR hard Correction as underlying events, rather than switch for our ISR hard processprocess

MSTP 91: Primordial Kt distribution of parton in protons. Default=1 as Gaussian dist. Switch to 0 as no Kt correction. Gaussian distribution with peak around ~400MeVGaussian distribution with peak around ~400MeV

These MSTP parameters are corrections happened after “hard process”. While CKIN3 is cut in the “hard process”

23/4/21 DTY bi-weekly meeting, J. Zhong 12

Meaning of CKIN3discussion in MC hyper news (cont. 2)

Cross section not changed by these corrections.

The tail was eliminated mainly by switching off ISR

Less significant effect from Kt dist.

Even output file size will be reduced by stop ISR.

MSTP61=0 & MSTP91=0

MSTP61=d & MSTP91=d

MSTP61=0 & MSTP91=d

MSTP61=d & MSTP91=0

23/4/21 DTY bi-weekly meeting, J. Zhong 13

Meaning of CKIN3discussion in MC hyper news (cont. 3)

The four momentum of incoming and outgoing particles are not conserved.

KEndVNt==4 as incoming particles, 1 & 2

KOriVNt==4 as outgoing particles, 3 & 4

Boost particle 3&4 (Z+gamma) to the 1+2 (incoming quarks) rest frame.

Plot entries over ln[Pt(Z+gamma)]

A peak around 6, namely ~400MeV

Broad distribution up to hundreds GeV.

23/4/21 DTY bi-weekly meeting, J. Zhong 14

Meaning of CKIN3discussion in MC hyper news (cont. 4)

In the rest frame of incoming quarks and gluons, Pt of W+gamma has a distribution, rather than flat zero if four momentum are conserved

The peak is at ~400MeV, which is around the peak of Kt distribution correction.

Indicates inconsistency of data documentation between incoming and outgoing particles, in different stages (before or after Kt dist. correction)

There was similar report earlier in generator HN.

This may be the reason of CKIN3 shift. Athena Generator group will investigate into it.

23/4/21 DTY bi-weekly meeting, J. Zhong 15

Further discussionISR in hard/soft process

In our attempt, we turned off the ISR switch. And the cross-section didn’t have noticeable deviation.

Though in physics, this ISR as correction is the same Feynman diagram as our ISR process (t-channel of VPhoton), in Pythia they are two different conceptions.

Maybe it’s more exact to turn off the ISR switch for our ISR hard process

Is there some potential trouble by comparing the hard process ISR in VPhoton and the soft ISR correction in V-inclusive samples?

23/4/21 DTY bi-weekly meeting, J. Zhong 16

Validation in Version 13 No support in version12 for new sample validation

anymore.

Need version 13, which use latest Pythia version

Test run with transformation is successful in a local installation

Joboption to convert EVNT into CBNT has failed. Need to find a solution

23/4/21 DTY bi-weekly meeting, J. Zhong 17

Conclusion Lower Pt cut can give more phase space for study.

Comparison of the cross-section reveals discrepancy with cross-section, and further questions that we omitted before.

Pythia_i need to be investigated, especially data documentation needs some check.

Need more understanding of how generator works, rather than use everything as a black box.